1. Field of the Invention
This invention generally relates to a device authentication system for verifying that an accessory device connected to a main device is genuine or legitimate to the main device. This invention specifically relates to a device authentication system for verifying that a battery connected to a video camera is genuine or legitimate to the video camera. This invention also relates to an authenticating device and a device to be authenticated. Furthermore, this invention relates to a method used by a device authentication system or an authenticating device.
2. Description of the Related Art
It is recommendable to use a genuine device as an accessory device connected to a main device in operation reliability, safety, and performance. In the case of video cameras, there are accessory batteries specified by video camera makers. It is desirable that such a specified battery is used as an accessory battery connected to a video camera.
Japanese patent application publication number 11-8618/1999 discloses a device authentication system in which first and second devices have a same group of private keys. The first device generates a random number, and encrypts the generated random number with one of the private keys to generate a first encrypted random number. The first device sends the first encrypted random number to the second device. The second device decrypts the first encrypted random number through the use of the private key group to generate a decrypted random number. The second device encrypts the decrypted random number with one of the private keys to generate a second encrypted random number. The second device returns the second encrypted random number to the first device. The first device decrypts the second encrypted random number through the use of the private key group to generate a recovered random number. The first device compares the recovered random number with the original random number. When the result of the comparison indicates that the recovered random number is equal to the original random number, the first device concludes the second device to be legitimate.
In the device authentication system of Japanese application 11-8618/1999, the encryption and decryption using the private key group necessitate complicated computation procedures, and cause a great data processing load. Therefore, the first device takes a long time to authenticate the second device. It is necessary to equip each of the first and second devices with a nonvolatile memory storing the group of the private keys.